is_valid_iban.py

VALID_LENGTHS = dict()
for s in open("is_valid_iban_data.txt").read().split("\n"):
    VALID_LENGTHS[s[:2]] = int(s[3:])


def is_valid_iban(string):
    iban = string.replace(" ", "").replace("-", "").upper()
    if  len(iban) == VALID_LENGTHS[iban[:2]]:
        inverted_iban = iban[4:] + iban[:4]
        number = ""
        for c in inverted_iban:
            if "A" <= c <= "Z":
                number += str(ord(c)-55)
            elif c in "0123456789":
                number += c
            else:
                return False
        return int(number) % 97 == 1

Oui, c'est ça!